Field of the Invention
The present invention relates to air driven structures useful in the recovery of precious ore deposits from ground formations located in arid sites, commonly referred to as dry washers, and more particularly to improvements in the agitation mechanisms thereof to promote concentration of ore bearing particulates and their retention within structures deployed in a dry washer to assist in their recovery.
Description of the Prior Art
Both the natural accumulation processes of precious metal deposits, like silver or gold, and also their eventual mining and collection, rely on the unique attributes thereof such as a high specific gravity, low melting point and/or limited chemical reactivity, with their high relative density providing the primary selection and concentration mechanism in low cost, remotely located, placer mining. The familiar image of a prospector panning on the banks of a remote stream is therefore symbolic of gold prospecting, often displayed in exotic, well irrigated settings surrounded by bountiful vegetation and animal life.
While perhaps there once were such verdant settings in the distant past where gold may have been found, at this time the offensive aspects of aggressive mining have produced a multitude of regulatory constraints that then combined with a landscape already depleted, relegating most current mining activity to very remote, infertile, barren locations irrigated by few, or no local water flows. Instead, the current low-investment mining efforts have all shifted to marginal, arid and otherwise useless sites that are best worked by dry washer processes, sometimes referred to as dry placer mining, as exemplified in U.S. Pat. No. 1,701,624 to Lide; U.S. Pat. No. 3,773,174 to Stimpel; U.S. Pat. No. 4,451,357 to LaVigne; U.S. Pat. No. 4,615,797 to Keene; and many others.
Generally, these prior art dry washers each include some form of a classifying hopper at theirs inputs each provided with a classifying screen onto which the prospected local particulates are shoveled to then pass their smaller sized ones onto its smooth, inclined bottom surface to slide down into an inclined dry washer chute, or dry sluice, that includes a smooth bottom surface spaced below a fibrous mat that itself is supported on a perforated, air-permeable diffuser panel. A pumped current of air is then conveyed through this smooth bottom surface of the chute from below, either directly from an attached air pump, or by way of conveying channels, to ventilate the fibrous mat with the particulates collected therein, with the pumping mechanism and/or its air flow turbulence imparting agitation to the assembly that promotes the descent of the higher density particulates into and/or through the mat to be thereafter collected in a collection vessel.
Of course, fluid flow mechanisms similar to those used in water flows through a sluice assembly are also applicable in an air driven process and various riffle structures are utilized to promote particulate propagation into and through the fibrous mat. Significantly, however, the fluid dynamic forces associated with moving air are substantially less intense than those of water and the use of a dry washer is therefore more dependent on the efficient use of energy to drive the agitating movements through its structure to promote particulate collisions and consequent fractioning into particulates that have surface to mass ratios that are responsive to aerodynamic flows. This fractioning process invariably entails large parasitic frictional losses as the aggregate is moved around on the dry washer surfaces, with these same high friction levels then damping the several modes Of elastic motion in the dry washer structure itself. Thus, like in the familiar engineering school experiment where an elastic structure on a shaker table will quickly display its node lines when just lightly sprinkled with sand, when the sand load is excessive its damping fully submerges all definition of the elastic modes and added resonant structures that are above the sand layers may be required.
Mechanisms that limit these inherent deficits of the dry placer mining process are therefore extensively desired and it is one such mechanism that is disclosed herein.